Plasticized polyvinyl acetate emulsion



Patented Dec. 11, 1951 PLASTICIZED POLYVINYL ACETATE EMULSION Howard 0.Brinker, South St. Paul, Minn., a-

Delaware signor to Minnesota Mining & Manufacturing Company, St. Paul,Minn.,

a corporation of No Drawing. Application January 31, 1951,

Serial No. 208,850

16 Claims. (01. 260-27) This invention relates to materials for coatingsheet materials, particularly paper and cardboard, to render them greaseresistant or greaseproof, and for forminggrease resistant or greaseprooffilms.

Polyvinyl acetate emulsion or dispersion is such a, material butheretofore the known plasticizers for it necessary to render it suitablefrom the point of view of flexibility, have been unsatisfactory,primarily because they themselves must first be emulsified before theycan be used. This requires an additional step in the process ofmanufacture; it also results in the water dilution of the polyvinylacetate emulsion so as to render impossible the production ofhigh-solids emulsions. It is of course well known that highsolidsemulsions are highly desirable in coating processes. Many previousplasticizers have also been unsatisfactory because they are volatile, soas to be partially or wholly driven off if heat curing of the materialwhich they are intended to p-lasticize, is employed.

Objects of the invention therefore include the provision of aninexpensive easily used plasticizer for polyvinyl acetate emulsion thatwill not dilute it, that is non-volatile and that will render itsuitable for coating flexible porous sheet materials to render themgreaseproof, and for forming grease resistant or greaseproof films.

The invention provides a plasticizer that contains an ester group and afree hydroxyl group. The ester group provides compatibility with thepolyvinyl acetate and the hydroxyl'group provides dispersability inemulsions.

More particularly the invention provides a partial ester of a polyhydricalcohol and abietic acid,

- such as a monoester of a glycol and an abietic acid from rosin, i. e.,glycol monoabietate, an example of which latter maybe prepared asfollows:

The polyethylene glycol in the above example has an average molecularweight of 300. The

rosin is preferably gum rosin, but wood rosin may be used.

Heat at atmospheric pressure in a flask connected to acondenser and awater separator. Xylol is added in suflicient quantity for azeotropicremoval of the water formed during esterification. The heated mixturemay be stirred if desired and an inert gas blown through to keep 2 xylolare drawn oil as an azeotrope and condensed. The water is separated andthe xylol returned to the flask.

The preferred temperature for esterification is 500 F.i15. When 18 to 20cc. of water has been separated the monoester is formed. The excessxylol is removed and the monoester is allowed to cool. The final producthas an acid number of 35:15 and a viscosity at to F. of 13002200centipoises.

Any glycol may be used. those readily esterifiable with rosin beingpreferred. Examples of such include ethylene glycol, di ethylene glycol,tri ethylene glycol, etc.; propylene glycol, dipropylene glycol. etc.The plasticizers from lowered molecular weight glycols tend to produce aproduct somewhat less flexible than when higher molecular weight glycolsare used.

Other esterification catalysts such, for example as zinc chloride, zincacetate and sodium acetate may be used.

The above esterification products of glycol and rosin consist of stableliquid monoesters of rosin; have a terminal hydroxyl group at the end ofa long chain; are soluble in organic solvents, are self dispersable inwater as well as in emulsions of polyvinyl acetate and do not bleedtherefrom; are non-volatile; have a low vapor pressure; havesubstantially no odor; are easily prepared. They are particularlysuitable as plasticizers for polyvinyl acetate emulsion.

Examples of polyhydric alcohols in addition to the glycols, that may besimilarly esterified with rosin to produce plasticizers for polyvinylacetate emulsion, include glycerine, sorbitol, penta erythritol andmannitol.

The plasticizers of thisinvention may be added directly to polyvinylacetate emulsions simply by warming slightly to lower the viscosity andthen stirring into the emulsion.

They do not need themselves to be emulsified or otherwise treated.Polyvinyl acetate emulsions, thus plasticized, consequently remainundiluted.

'l'he plasticized polyvinyl acetate emulsions of this invention formcontinuous films that are soft and flexible and may be coated ontoflexible sheet material without materially lessening the degree offlexibility of the uncoated sheet. They are particularly suitable forcoating sheet material to render it greaseproof or grease resistant;they may also be formed into self-sustaining films.

out'air and retain a light color. The water and 55 The term "grease"hereinisintended toinclude 7 3 mineral, animal and vegetable greases.fats and oils.

The application or the plasticlzed emulsion to sheet material may bemade according to known coating procedure. e. 3., it may be warmedslight- 1y, coated onto the sheet material, and then dried either atroom or elevated temperatures until it forms thereon a flexible fllm.The coating weight may vary.

Grease resistant barrier wrap or grease resistant barrier board suitablefor the manufacture oi grease resistant packages. cartons andcontainers, may be formed by coating the plasticized polyvinyl acetateemulsion on to paper or cardboard, respectively, and then drying. Forsuch purposes the emulsion is preferably plasticized by addingapproximately 20 parts of the plasticizer to approximately 100 parts 01'the emulsifled polyvinyl acetate, the parts being by weight based on thetotal solids content. An average coating weight or 9 to grains per 4" x6" area and a drying temperature of 120 F. is satisfactory. The greaseresistant barrier board may also be formed 01' laminations or the paper.the board, and the resinous coating or film.

The emulsion may be cast. extruded or otherwise formed, according toknown procedures, into self-sustaining fllms.

This is a continuation-impart of my copending application Serial No.69,047 flied January 3, 1949, now abandoned.

I claim:

1. Polyvinyl acetate emulsion plasticized with a composition comprisingan ester 01' a polyhydric alcohol and abietic acid having at least oneunreacted hydroxyl group.

2. A flexible film comprising the dried residue of the composition oi.claim 1.

3. Sheet material coated with the composition of claim 1.

4. Grease resistant barrier board comprising 4 cardboard coated with thecomposition of claim 1. 5. Polyvinyl acetate emulsion plasticized with acomposition comprising a monoester ot a s ycol and abietic acid having aterminal hydroxyl group.

6. A flexible fllm comprising the dried residue or the composition orclaim 5.

13. Polyvinyl acetate emulsion plasticized witha composition comprisingan ester of sorbitol and a-bietic acid having at least one unreactedhydroxyl group. 4

14. A flexible fllm comprising the dried residue of the composition ofclaim 13.

15. Sheet material coated with the composition of claim 13.

16. Grease resistant barrier board comprising cardboard coated with thecomposition or claim 13. I

HOWARD p. BRINKER.

REFERENCES CITED The following references are of record in the tile ofthis patent:

UNITED s'ra'rrzs PATENTS Name Date Smith Feb. 29, 1944 Number

1. POLYVINYL ACETATE EMULSION PLASTICIZED WITH A COMPOSITION COMPRISINGAN ESTER OF A POLYHYDRIC ALCOHOL AND ABIETIC ACID HAVING AT LEAST ONEUNREACTED HYDROXYL GROUP.